The present invention relates generally to catheters for use in blood vessels or other body canals. More particularly, the present invention relates to a catheter having a "non-balloon" expandable segment wherein the expandable segment is actuated by the use of compressive forces applied to a series of bands which deform in a predetermined fashion, thereby expanding to an infinite number of diameters. The present invention may be used to implant stents but, also, has a variety of uses wherein a stent is not utilized in the procedure.
The prior art includes balloon catheters as well as the Krumme U.S. Pat. No. 5,409,460 which relates to a non-balloon expander assembly.
The Krumme patent teaches a system having several serious drawbacks. First, the patent discloses an expander assembly having a core element sensitive to temperature changes and the expansion is caused by the application of heat to electrical resistance elements which in turn heat the metal. The application of heat and electrical voltage inside the lumen creates a variety of possible adverse medical complications. Furthermore, the Krumme design is incapable of use with a guide wire. As a practical matter, incapability with a guide wire renders the device practically useless in coronary vessels and the device shown in the Krumme patent has not been built or commercialized.
The prior art also includes balloon catheters. Balloon catheters are well-known medical devices with an inflatable balloon attached to the distal end of a catheter. Positioning and inflation of the balloon within a body space (usually a vessel) results in dilation of the body space. Over the last twenty years, balloon catheters have become widely accepted for use in a medical procedure called Percutaneous Transluminal Coronary Angioplasty (PTCA), first introduced by Andreas Gruent-zig in 1977. Balloon catheters for angioplasty are typically made out of thin walled, high tensile strength materials with relatively low resilience. The materials used in angioplasty are flexible with varying degrees of elasticity (compliance). The noncompliant balloon will readily inflate to a predetermined diameter at normal pressures. The more compliant balloon allows some flexibility in diameter achievement.
The success of the angioplasty procedure has, unfortunately, included some significant and life threatening problems. Patients with arteriosclerotic disease who undergo balloon angioplasty are at risk for abrupt vessel closure and acute dissection. In the event of a partial or total occlusion of a coronary artery from a blood clot or from dissection of the arterial lining, the patient's life may be jeopardized. Immediate medical intervention often is required. Even if angioplasty is initially successful, as many as 40% of many patients experience restenosis of the treated artery.
Due to the above problems, recent efforts have led to the development of endoprosthetic devices, commonly called stents. Stents are metallic cylindrical devices, deployed by a balloon in the artery at the lesion location in order to maintain the artery's patency. Today, the most commonly used stent delivery system was developed by Johnson & Johnson International Systems. This system, which is based on conventional balloon catheter technology, disposes a balloon expandable stent crimped onto a folded, non-inflated balloon. The catheter is introduced percutaneously through the femoral artery into the patient's cardiovascular system until the stent is located at the lesion site. Balloon inflation causes the stent to expand and dilate the artery. The final step in the procedure is to deflate the balloon and to retract the catheter, leaving the stent in place. Since the stent is designed such that it will not compress once it expands, the artery is held open by the radial strength of the stent.
Although the use of a stent overcomes some of the problems associated with angioplasty, the use of balloon catheter technology to expand the stent has resulted in other potential complications, which may arise during implantation of the stent:
1. As the balloon inflates to expand the stent, the distal end of the balloon inflates outside the longitudinal boundary of the stent, potentially resulting in serious damage to the artery.
2. If the balloon, which is typically very thin walled, develops a leak, the balloon material may result in incomplete stent deployment and may make catheter extraction more difficult.
3. Lack of uniform unfolding of the balloon may result in a asymmetrical expansion and incomplete dilation.
4. The stent may slide off the balloon and embolize distally making extraction difficult and exposing the patient to serious, life threatening consequences.
Another significant limitation in the use of a balloon catheter to deploy a stent results from the need to determine precisely the correct stent diameter to be used for the procedure. Often additional balloons are required to achieve the correct stent expansion.
In short, surgeons need a stent delivery and removal apparatus and system that overcomes the limitations of the balloon catheter system by providing a system which is safer, more efficient, less wasteful, and provides the surgeon with a range of procedural options which do not exist with the current stent delivery technology.
The present invention provides a new and unique catheter design that avoids the limitations inherent in the design of the Krumme U.S. Pat. No. 5,409,460 and which avoids the problems associated with the conventional balloon catheters as used either with or without stents. In general, the present invention is capable of use with guide wires and does not require the application of heat to the expander, the use of special heat sensitive alloys or the use of electrical voltages inside the lumen. The present invention utilizes an expandable segment having a plurality of longitudinally extending bands wherein each of the bands has a plurality of predesigned buckle points. When compressive axial forces are applied to the bands, the bands expand at the buckle points. The bands may be expanded to an infinite variety of diameters, in sharp contrast to conventional balloon catheters.
The present invention also includes several advantages over the prior art when used in conjunction with a stent. For example, the present invention can deliver several stents of different lengths simultaneously. One or more of the stents can be implanted in a single procedure without removing the catheter to implant a second or third stent.
The invention also provides the surgeon with a more precise and flexible procedure for implanting stents in a patient's artery. Current balloon catheter technology requires the surgeon to select a predetermined stent and balloon size. The balloon must completely inflate in order for the stent to expand properly. If the surgeon selects a stent having a diameter that is either too large or too small, problems can arise. If the expanded stent is too small, the likelihood for restenosis is greater. On the other hand, if the stent diameter is too large, the stent may cause serious damage to the artery. The present invention overcomes these problems by providing the physician with the means to expand the stent in a controlled manner and potentially over a larger range of stent diameters.
Another feature of the present invention includes a multi-tasking feature including a stent preparation segment and a separate stent delivery segment wherein the stent preparation segment is substantially identical to the stent delivery segment with the exception that a stent is not disposed around the tube. The stent preparation segment, when expanded at a lesion site, opens the artery in order to prepare the artery for insertion of the stent. The stent preparation segment may similarly be incorporated as part of a multi-tasking tube and, in a preferred embodiment, the stent preparation segment is located on the distal end of the tube. The tube may also contain a medication chamber, which may be expanded in a manner similar to the expansion of the stent delivery segment and, thereby, cause medicine to be released at a needed location within a body lumen.
Another feature of the present invention is that the stent delivery segment may be used to deliver other endoprosetic devices, such as stents of various expanded shapes and configurations to be used in tapered or asymmetrical body lumens. A particularly significant application is to use the invention to implant a stent-plug within an artery, which is providing blood to a cancerous tumor so as to block the supply of blood to the tumor, causing the tumor to die.
The above-described novel stent delivery apparatus and system has a particularly novel and useful application to its use in the surgical implantations of stents within a patient's cardiovascular system, because the invention overcomes some of the serious life threatening limitations of present balloon catheter stent implantation technology. It should be apparent that the present invention does not exhibit any of the problems associated with the use of a balloon, since the sealed balloon is replaced with an elongated tube having an expandable section. This expandable section expands symmetrically away from the tube's axis when a slight compressive force is applied to the tube in an axial direction. Thus, the stent cannot slide off the tube due to asymmetrical expansion. It should also be apparent that the invention cannot leak, like the balloon, because the unique stent apparatus and delivery system uses a physical force, rather than a radiocontrast material (fluid) to expand the stent.
The present invention differs from balloon catheters in the significant respect that, whereas balloon catheters require the use of relatively high pressure to expand the balloon, the present invention utilizes less than half the pressure, reducing the risk of rupturing or tearing the lumen wall.
Another significant advantage of the present invention is that the expansion segment has longitudinal flexibility and may be utilized in a curved portion of a blood vessel or other lumen. Prior art balloon catheters use relatively high pressure to expand the balloon and may involve significant risk when used in a curved artery or other lumen.
A primary object of the invention is to provide a catheter with a safer, more reliable and improved "non-balloon" expansion mechanism, as described above.
A further object is to provide a catheter with one or more expandable segments for use with or without stents, as described above.
Further objects and advantages will become apparent from the above summary and the following description and drawings, wherein: